Search Publications
NLTE analysis of the unique pre-white dwarf H 1504+65.
Werner, K.
High S/N optical spectra and line profile fits with line-blanketed non-LTE model atmospheres show that H 1504 + 65 is the hottest star ever analyzed by model atmosphere methods. It is also noted that the atmospheric composition of this prewhite dwarf is almost entirely carbon and oxygen by equal parts, and that it is virtually devoid of H and He. …
Interpretation of the ion mass spectra in the mass per charge range 25-35 amu/e obtained in the inner coma of Halley's comet by the HIS-sensor of the Giotto IMS experiment
Altwegg, K.; Balsiger, H.; Geiss, J. +6 more
The IMS-HIS double-focusing mass spectrometer that flew on the Giotto spacecraft covered the mass per charge range from 12 to 56 (amu/e). By comparing flight data, calibration data and results of model calculations of the ion population in the inner coma, the absolute mass scale is established, and ions in the mass range 25 to 35 are identified. I…
Ultraviolet Interstellar Absorption toward HD 156359, a Halo Star at 11 Kiloparsecs in the Direction L = 329 degrees and B = -15 degrees
Sembach, Kenneth R.; Savage, Blair D.; Massa, Derck
Results based on high-quality multiple IUE high-dispersion spectra are presented for the HD 156359 sight line in the direction l = 328.7 deg and b = -14.5 deg. The UV stellar spectrum of HD 156359 is consistent with an MK classification of O9.7 Ib-II. The high-ionization UV interstellar absorption line in the star's UV spectrum are very broad with…
Classical Cepheid Luminosities from Binary Companions
Evans, Nancy Remage
Luminosities for the classical Cepheids Eta Aql, W Sgr, and SU Cas are determined from IUE spectra of their binary companions. Spectral types of the companions are determined from the spectra by comparison with the spectra of standard stars. The absolute magnitude inferred from these spectral types is used to determine the absolute magnitude of th…
Weighted Slit Extraction of Low-Dispersion IUE Spectral Data
Bohlin, R. C.; Kinney, A. L.; Neill, J. D.
standard extraction for low-dispersion spectra in the final IUE archives. In order to properly weight the data within the extraction slit and obtain the optimal evaluation of the true spectrum, a noise model is derived for IUE data. The exclusion of cosmic rays is demonstrated and the improvement in signal-to-noise ratio is quantified for spectra …
Non--LTE Analysis of the Ofpe/WN9 Star HDE 269227 (R84)
Leitherer, Claus; Schmutz, Werner; Hubeny, Ivan +3 more
The paper presents the results of a spectral analysis of the Ofpe/WN9 star HD 269227 (R84), which assumes a spherically expanding atmosphere to find solutions for equations of radiative transfer. The spectra of hydrogen and helium were predicted with a non-LTE model. Six stellar parameters were determined for R84. The shape of the velocity law is …
Discovery of a Fast Radiative Shock Wave in the Cygnus Loop Using the Hopkins Ultraviolet Telescope
Ferguson, Henry C.; Blair, William P.; Gull, Theodore R. +12 more
Observations of the far-ultraviolet spectrum of a bright radiative filament on the eastern edge of the Cygnus Loop supernova remnant are described which were made through the Hopkins Ultraviolet Telescope aboard the Astro-1 Space Shuttle mission in December 1990. Observations include strong emission lines of C III 977, N III 991, and O VI 032, 103…
New Observations of the Gas Cloud Associated with the Quasar-Galaxy Pair 3C 232/NGC 3067
Donahue, Megan; Shull, J. Michael; Stocke, John T. +2 more
We present new optical Na I and Ca II spectra, new Hα images, and archival IUE ultraviolet spectra of the quasar-galaxy pair 3C 232/NGC 3067, to study the H I gas cloud seen in 21 cm emission between the eastern edge of NGC 3067 and 3C 232. High-resolution optical spectra show two, and possibly three, absorption systems in Ca II and Na I, with a l…
Emission from Dust in Visual Reflection Nebulae at Infrared and Submillimeter Wavelengths
Casey, Sean C.
Far-IR and submillimeter images of five bright visual reflection nebulae, IC 446, NGC2247, NGC 2245, NGC 7023, and CED 201 are presented and used with composite IR spectra to derive parameters such as the fraction of nebulae emission attributed to molecule-sized grains, the range of nebulae grain albedos, gas densities, and gas cloud geometries. T…
On the evolutionary link between white dwarfs and central stars of planetary nebulae : NLTE analysis of PG 1144+005.
Werner, K.; Heber, U.
Line-blanketed non-LTE (NLTE) model atmospheres are used to study the optical spectra of the hydrogen-deficient prewhite dwarf PG 1144 + 005 by means of a spectral analysis. The star is compared to a prototype PG 1159 star for the analysis, and the stellar parameters of the PG 1144 dwarf show that the N/O ratio is indicative of very strong nitroge…